Balancing the Unbalanced: The Story of the Inverted Pendulum Project
Ever seen a broom balanced on someone’s finger? That’s the vibe behind one of engineering’s trickiest and coolest challenges: the inverted pendulum. The inverted pendulum problem isn’t just a balancing act—it’s a prime example of real-world control systems, teaching budding engineers how to stabilize things that naturally want to fall over. While most engineering students only encounter it in the classroom, a dedicated team of students from the University of Rhode Island (URI) and Germany's Technical University of Darmstadt (TU) took it further. They brought it to life, designing, building, and implementing an inverted pendulum system in two identical setups on different continents and working together virtually.
The project aimed to create an inverted pendulum system that serves as a launchpad for control system studies, future projects, and joint research. Picture it: a testbed that’s a goldmine for experimenting with control theories and techniques that could one day help stabilize more complex systems, from robots to drones.
Why the Inverted Pendulum?
The inverted pendulum is a favorite among control theorists. It’s unstable by nature (unlike your typical pendulum that hangs down and swings predictably). This system constantly requires correction to keep it balanced—a fun but tough challenge that mirrors real-life control problems. By monitoring the pendulum’s angle and position through sensors, the system’s controller makes tiny adjustments to an actuator that moves the cart holding the pendulum. This feedback loop gives engineers the power to keep the pendulum steady.
With the pendulum’s non-linear, unpredictable behavior, it’s perfect for testing cutting-edge control strategies.
Laying the Groundwork: Preliminary Design
Before getting hands-on, the URI and TU teams mapped out their design goals and system requirements. They listed everything they wanted this system to accomplish and how it needed to behave in action. Here are some key targets:
- Performance Specs: The state-feedback controller had to keep the pendulum within tight stability margins and meet criteria like phase margin, gain margin, and robustness.
- Pendulum Stability: Maintain an upright position within ±2° and stay within ±50 mm of the starting position, even after moderate pushes.
- Controller Flexibility: The system had to support various control types.
- Build Specs: They ensured a minimum rail travel, compatible power requirements, and corrosion-resistant materials.
- Safety First: The team added mechanisms like an emergency power shut-off and derailment prevention.
These requirements ensured that the system would be safe, reliable, and sturdy enough to handle rigorous tests without breaking down.
Building the System
With the plans in place, it was time to gather materials. The team analyzed the best mechanical components, especially the rail and carriage system, which needed to be both low-maintenance and able to withstand plenty of future use. Using principles of kinematics and dynamic equations, the team refined specifications for the motor's speed and torque, essential for keeping the system balanced. Finally, they selected brushless DC motors, striking a balance between performance and budget.
AMC Steps In
The team reached out to ADVANCED Motion Controls (AMC) for help in powering their creation. AMC, committed to supporting academic research, reviewed the project’s potential benefits and technical challenges. After careful consideration, AMC provided two BE12A6 PWM servo drives (one for each school's setup). These advanced drives power the motors that respond to control signals, keeping the pendulum in check even under tough conditions.
Testing and Simulations
Before risking the real hardware, the students ran simulations to fine-tune the controller. Using Simulink, they tested how well the state-feedback system would handle disturbances. With solid results in simulation, they felt ready for real-world trials.
Real-World Trials: Stability and Stress Tests
The big test came with live trials, starting with a 240-second stability test. The team then moved to stress tests, where they applied increasingly intense “nudges” to see if the pendulum would regain its balance. Each time the cart returned to its starting position, they amped up the disturbances until, at last, the system reached its tipping point.
Results and Lessons Learned
The inverted pendulum successfully recovered from moderate disturbances, with the system only hitting its limits when the pushes got extreme. These tests validated the controller’s effectiveness and highlighted areas to improve. With real data in hand, the students completed a project that wasn’t just about building—it was about exploring the limits of control theory.
The Road Ahead
After 16 weeks of research, planning, and testing, the URI and TU teams delivered a test bench that future engineers and researchers can use to develop control strategies. With potential applications in robotics, AI, and even machine learning, this platform opens doors for exploring control methods that could lead to the next big thing in engineering.
The inverted pendulum project is proof that even when working virtually, students from around the world can come together to tackle complex problems—and have fun doing it. And who knows? This wonky, wobbly pendulum might just be the spark that inspires the next generation of innovation in control systems.
